In an internal combustion engine, a throttle is a valve that directly regulates the amount of air entering the engine, indirectly controlling the fuel burned in each cycle due to the fuel-injector or carburetor maintaining a relatively constant fuel/air ratio. Generally a throttle is a type of quarter-turn butterfly valve which has a rotatable rod passing through it. The throttle rotates with the rod through a predetermined angle, such as 90 degrees, with 0 degree rotation corresponding to the completely closed state and 90 degree rotation corresponding to fully open state.
FIG. 6 illustrates a throttle control module 20 which comprises throttle position sensors (TPS) 21, pulse-width modulation (PWM) module 22, motor controller 23, brush type permanent magnet direct current (PMDC) motor 24 and a gear train 25. The sensor 21 detects the position of the throttle and generates a throttle position signal. The PWM module 22 generates a PWM sequence according to the throttle position signal and a desired position signal provided by an engine control module (ECM). As is known, an ECM, also known as engine control unit (ECU) or power-train control module (PCM), is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. The motor controller 23 controls the PMDC motor 24 according to the PWM sequence so that the PMDC motor 24 as well as the gear train 25 can control the opening or position of the throttle 10. As is known, the throttle rotates repeatedly within a predetermined angle such that only some of the commutator segments will frequently make sliding contact with the brushes. These segments as well as the PMDC motor will probably have a shortened life. In addition, an oxide film will build up on the copper segments which results in an increased resistance and an increased temperature. Furthermore, there is the risk of building up thin layers of carbon creating dead spots on the commutator segments especially on motors where the operating mode only sees interface contacts between brush and commutator of 2 or 3 segments in connection with high frequent position.
One proposed solution is to replace the motor with a brushless direct current (BLDC) motor. FIG. 7 illustrates a known throttle control module 30 for a BLDC motor 34 which is partly shown in FIG. 8. The motor 34 is shown partially exploded to reveal a rotor having a permanent magnet rotor core 34a and a sensor magnet 39, a wound stator 34b and a circuit board 38 supporting three Hall sensors 37. The Hall sensors provide signals indicative of the rotational orientation of the rotor based on the interaction of the Hall sensors and the sensor magnet 39. The throttle control module 30 comprises TPS 31, PWM module 32, motor controller 33, BLDC motor 34, gear train 35 and commutation logic module 36. The commutation logic module 36 generates commutation logic according to signals from Hall sensors 37 which are mounted inside the BLDC motor 34. The motor controller 33 controls commutation of the BLDC motor 34 according to the commutation logic and PWM sequence provided by the PWM module 32, so that the opening of the throttle 10 is controlled. For this proposal, the signals from the Hall sensors are critical. However, the ambient temperature where the BLDC motor 34 operates is often high and sometimes exceeds the normal operating temperature for the Hall sensors. Thus the Hall sensors and the throttle control module are not reliable. Furthermore, the throttle control module is costly as three Hall sensors 37 are required for the BLDC motor.